Transmission and reception of proximity detection signal for peer discovery

ABSTRACT

Techniques for performing peer discovery to enable peer-to-peer (P2P) communication are disclosed. In an aspect, a proximity detection signal used for peer discovery may be generated based on one or more physical channels and/or signals used in a wireless network. In one design, a user equipment (UE) may generate a proximity detection signal occupying at least one resource block based on a SC-FDMA modulation technique. In another design, the UE may generate a proximity detection signal occupying at least one resource block based on an OFDMA modulation technique. The UE may generate SC-FDMA symbols or OFDMA symbols in different manners for different physical channels. In yet another design, the UE may generate a proximity detection signal including a primary synchronization signal and a secondary synchronization signal. For all designs, the UE may transmit the proximity detection signal to indicate its presence and to enable other UEs to detect the UE.

The present application claims priority to provisional U.S. ApplicationSer. No. 61/324,619, entitled “PILOT OPTIONS FOR PEER-TO-PEER (P2P)DISCOVERY,” filed Apr. 15, 2010, and provisional U.S. Application Ser.No. 61/327,604, entitled “PEER-TO-PEER PROXIMITY DETECTION SIGNAL DESIGNAND UTILIZATION THEREOF,” filed Apr. 23, 2010, both incorporated hereinby reference in their entirety.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for supporting peer-to-peer (P2P)communication.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks. A wireless communication network may also be referred to as awide area network (WAN).

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station. The UE may also beable to communicate peer-to-peer with one or more other UEs. It may bedesirable to efficiently support P2P communication for UEs.

SUMMARY

Techniques for performing peer discovery to enable P2P communication aredescribed herein. In an aspect, a proximity detection signal used forpeer discovery may be generated based on one or more physical channelsand/or signals used in a wireless network. These physical channels andsignals may be designed to have good performance for WAN communicationand may thus provide good performance for peer discovery.

In one design, a UE may select at least one resource block from among aplurality of resource blocks reserved for transmission of proximitydetection signals by UEs. Each resource block may cover a set ofsubcarriers in a plurality of symbol periods. The UE may generate aproximity detection signal occupying the at least one resource blockbased on a SC-FDMA modulation technique, e.g., for transmission on aPhysical Uplink Shared Channel (PUSCH) or a Physical Uplink ControlChannel (PUCCH). The UE may generate the at least one SC-FDMA symbol indifferent manners for the PUSCH and PUCCH, as described below. The UEmay transmit the proximity detection signal to indicate its presence andto enable other UEs to detect the UE.

In another design, a UE may generate a proximity detection signaloccupying at least one resource block based on an OFDMA modulationtechnique, e.g., for transmission on a Physical Downlink Shared Channel(PDSCH) or a Physical Downlink Control Channel (PDCCH). The UE maygenerate the plurality of OFDM symbols in different manners for thePDSCH and PDCCH, as described below. The UE may transmit the proximitydetection signal to indicate its presence and to enable other UEs todetect the UE.

In yet another design, a UE may generate a proximity detection signalcomprising a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS). The UE may transmit the proximitydetection signal to indicate its presence. The UE may generate and/ortransmit the proximity detection signal such that the PSS and SSS in theproximity detection signal avoid collision with the PSS and SSStransmitted by a base station in a wireless network. This may beachieved in various manners as described below. The PSS and SSStransmitted by the UE may then be distinguishable from the PSS and SSStransmitted by the base station.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless network.

FIG. 2 shows a process for network-assisted peer discovery.

FIG. 3 shows an exemplary frame structure.

FIG. 4 shows a design of transmitting proximity detection signals.

FIG. 5 shows a proximity detection signal generated based on the PUSCH.

FIGS. 6A and 6B show proximity detection signals generated based on thePUCCH for different formats.

FIGS. 7A and 7B show proximity detection signals generated based on thePDSCH for two subframe types.

FIG. 8 shows a proximity detection signal generated based on the PDCCH.

FIG. 9 shows transmission of a proximity detection signal on anon-raster channel frequency.

FIG. 10 shows transmission of a proximity detection signal comprisingthe PSS and SSS.

FIGS. 11, 12 and 13 show proximity detection signals generated based ona positioning reference signal (PRS), a sounding reference signal (SRS),and a Physical Random Access Channel (PRACH), respectively.

FIGS. 14 and 15 show two processes for performing peer discovery basedon different physical channels.

FIG. 16 shows a process for performing peer discovery based onsynchronization signals.

FIG. 17A shows a block diagram of a design of a UE.

FIG. 17B shows a block diagram of a design of a base station.

FIG. 17C shows a block diagram of a design of a directory agent.

FIG. 18 shows a block diagram of another design of a UE, a base station,and a directory agent.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother wireless networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA), Time Division Synchronous CDMA (TD-SCDMA), andother variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856standards. A TDMA network may implement a radio technology such asGlobal System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), Ultra MobileBroadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal MobileTelecommunication System (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A), in both frequency division duplexing (FDD) andtime division duplexing (TDD), are new releases of UMTS that use E-UTRA,which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA,E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from anorganization named “3rd Generation Partnership Project” (3GPP). cdma2000and UMB are described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). The techniques describedherein may be used for the wireless networks and radio technologiesmentioned above as well as other wireless networks and radiotechnologies. For clarity, certain aspects of the techniques aredescribed below for LTE, and LTE terminology is used in much of thedescription below.

FIG. 1 shows a wireless network 100, which may be a LTE network or someother wireless network. Wireless network 100 may include a number ofevolved Node Bs (eNBs) and other network entities. For simplicity, onlythree eNBs 110 a, 110 b and 110 c, a network controller 130, and adirectory agent 140 are shown in FIG. 1. An eNB may be an entity thatcommunicates with the UEs and may also be referred to as a base station,a Node B, an access point, etc. Each eNB may provide communicationcoverage for a particular geographic area and may support communicationfor the UEs located within the coverage area. In 3GPP, the term “cell”can refer to a coverage area of an eNB and/or an eNB subsystem servingthis coverage area, depending on the context in which the term is used.In 3GPP2, the term “sector” or “cell-sector” can refer to a coveragearea of a base station and/or a base station subsystem serving thiscoverage area. For clarity, 3GPP concept of “cell” is used in thedescription herein.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG)). In the example shown in FIG. 1,wireless network 100 includes macro eNBs 110 a, 110 b and 110 c formacro cells. Wireless network 100 may also include pico eNBs for picocells and/or home eNBs for femto cells (not shown in FIG. 1).

Network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with the eNBs via a backhaul. The eNBs may also communicatewith one another via the backhaul. Directory agent 140 may support peerdiscovery by UEs, as described below. Directory agent 140 may be aseparate network entity (as shown in FIG. 1) or may be part of an eNB ornetwork controller 130.

UEs 120 may be dispersed throughout wireless network 100 and possiblyoutside the coverage of the wireless network. A UE may be stationary ormobile and may also be referred to as a station, a mobile station, aterminal, an access terminal, a subscriber unit, a device, etc. A UE maybe a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, asmartphone, a netbook, a smartbook, a tablet, etc. A UE may be able tocommunicate with eNBs, relays, other UEs, etc.

In the description herein, WAN communication refers to communicationbetween a UE and an eNB, e.g., for a call with a remote entity such asanother UE. A UE interested or engaged in WAN communication may bereferred to as a WAN UE. P2P communication refers to directcommunication between two or more UEs, without going through an eNB. AUE interested or engaged in P2P communication may be referred to as aP2P UE. A group of two or more UEs engaged in P2P communication may bereferred to as a P2P group. In one design, one UE in a P2P group may bedesignated as a P2P server (or a P2P group owner), and each remaining UEin the P2P group may be designated as a P2P client. The P2P server mayperform certain management functions such as exchanging signaling with awireless network, coordinating data transmission between the P2P serverand the P2P client(s), etc.

In the example shown in FIG. 1, UEs 120 a and 120 b are under thecoverage of eNB 110 a and are engaged in P2P communication. UEs 120 cand 120 d are under the coverage of eNB 110 b and are engaged in P2Pcommunication. UEs 120 e and 120 f are under the coverage of differenteNBs 110 b and 110 c and are engaged in P2P communication. UEs 120 g,120 h and 120 i are under the coverage of the same eNB 110 c and areengaged in P2P communication. The other UEs 120 in FIG. 1 are engaged inWAN communication.

P2P communication may offer certain advantages over WAN communication,especially for UEs located close to each other. In particular,efficiency may improve because the pathloss between two UEs may besubstantially smaller than the pathloss between either UE to its servingeNB. Furthermore, the two UEs may communicate directly via a singletransmission “hop” for P2P communication instead of via two separatetransmission hops for WAN communication—one hop for the uplink from oneUE to its serving eNB and another hop for the downlink from the same ordifferent eNB to the other UE. P2P communication may thus be used toimprove UE capacity and also to improve network capacity by shiftingsome load over to P2P communication.

One challenge in P2P communication is discovery/detection of peer UEs ofinterest within a particular range, e.g., within radio frequency (RF)range. In general, peer discovery may be performed based on one or moreof the following:

-   -   Autonomous peer discovery—a UE performs peer discovery by itself        without assistance from a network, and    -   Network-assisted peer discovery—a UE performs peer discovery        with assistance from a network.

For autonomous peer discovery, a UE may occasionally (e.g., periodicallyor when triggered) transmit a proximity detection signal (PDS) toindicate the presence of the UE. A proximity detection signal may alsobe referred to as a peer discovery signal, a peer detection signal, etc.A proximity detection signal may comprise a pilot or a reference signaland may carry certain information for a transmitter of the proximitydetection signal. Alternatively or additionally, the UE may detectproximity detection signals from other UEs near its proximity Autonomouspeer discovery may be relatively simple to implement by UEs. However,autonomous peer discovery may result in (i) severe interference when UEsare dense and close together and (ii) poor battery life when UEs aresparse and far away.

FIG. 2 shows a design of a process 200 for network-assisted peerdiscovery. A UE 120 x may register itself with directory agent 140 uponentering WAN coverage, e.g., upon detecting a macro cell in wirelessnetwork 100 (step 1). UE 120 x may provide pertinent information todirectory agent 140 as part of P2P registration. For example, UE 120 xmay provide identification information for UE 120 x, service informationfor services requested by UE 120 x and/or services provided by UE 120 x,location information for UE 120 x, etc. UE 120 x may perform P2Pregistration to advertise its services and/or to obtain services. UE 120x may send a P2P request at the time of P2P registration (step 2). TheP2P request may indicate services requested by UE 120 x and/or servicesprovided by UE 120 x. UE 120 x may submit a new P2P request or update anexisting P2P request at any time after P2P registration. A P2P requestmay also be implicit and not sent.

Directory agent 140 may perform P2P registration of UEs and may maintaina list of active P2P requests from these UEs. Directory agent 140 mayperform request matching, which may include examining the P2P requestsfrom different UEs and identifying UEs with matching P2P requests (step3). Request matching may be performed based on various criteria such asthe services requested or provided by the UEs, the capabilities of theUEs, the locations of the UEs, etc. For example, a match may be declaredbetween UE 120 x and UE 120 y due to UE 120 x providing a service thatis requested by UE 120 y, or vice versa. A match may also require thetwo UEs to be within RF proximity of one another, which may bedetermined based on location information provided by the UEs during P2Pregistration.

If a match is found for UE 120 x, then directory agent 140 may send anotification of the match to UE 120 x (step 4 a). Directory agent 140may also notify UE 120 y, which may be part of the match for UE 120 x(step 4 b). The match notifications may inform UEs 120 x and 120 y toinitiate peer discovery, if needed. The match notifications may alsoconvey resources and/or other parameters to use for peer discovery. UEs120 x and 120 y may perform peer discovery in response to receiving thematch notifications from directory agent 140. For peer discovery, UE 120x may transmit a proximity detection signal to indicate its presence(step 5), and UE 120 y may detect the proximity detection signal from UE120 x (step 6). Additionally or alternatively, UE 120 y may transmit aproximity detection signal to indicate its presence (step 7), and UE 120x may detect the proximity detection signal from UE 120 y (step 8).

FIG. 2 shows a design of network-assisted peer discovery using directoryagent 140. Network-assisted peer discovery may also be performed inother manners. Network assistance may also be provided in transmissionand reception of proximity detection signals. In one design, fortightly-controlled network-assisted peer discovery, a network (e.g., aneNB or directory agent 140) may determine which P2P UE should transmitand/or which P2P UE should receive proximity detection signals, whichresources to use to transmit or receive the proximity detection signals,which signals to use for the proximity detection signals, etc. In onedesign, for loosely-controlled network-assisted peer discovery, thenetwork may reserve some resources (e.g., time, frequency, code and/orother resources) for proximity detection signals and may inform the P2PUEs (e.g., via broadcast information). A transmitting P2P UE may (e.g.,randomly) select some of the reserved resources and may transmit itsproximity detection signal based on the selected resources. ReceivingP2P UEs may search all reserved resources to detect proximity detectionsignals from transmitting P2P UEs. Tightly-controlled network-assistedpeer discovery may provide better interference management whileloosely-controlled network-assisted peer discovery may be lessburdensome on the network side and may also have less signalingoverhead.

Network assistance may also be provided for communication between P2PUEs after peer discovery. In one design, P2P UEs may measure receivedsignal strength of proximity detection signals from detected P2P UEs andmay send pilot measurement reports to the network. The network mayselect P2P communication or WAN communication for the P2P UEs based onthe pilot measurement reports and/or other information. The network mayalso assign resources for P2P communication between P2P UEs.

Network-assisted peer discovery may result in better control ofinterference and may also save power at P2P UEs. However,network-assisted peer discovery would not work for the UEs outside thecoverage of the network. In one design, network-assisted peer discoverymay be used when available (e.g., when in network coverage), andautonomous peer discovery may be used when network-assisted peerdiscovery is unavailable. Autonomous peer discovery may be used withoutany network control or coverage.

For both autonomous and network-assisted peer discovery, a UE maytransmit a proximity detection signal to indicate its presence andfacilitate its discovery by other UEs. It may be desirable to utilize aproximity detection signal having good performance and also simplifyprocessing to transmit and/or receive the proximity detection signal.

In an aspect, a proximity detection signal may be generated based on oneor more physical channels or signals used in a wireless network. Thesephysical channels and signals may be designed to have good performancefor WAN communication and may thus provide good performance for peerdiscovery. These physical channels and signals may also be transmittedand/or received by UEs for WAN communication. Hence, the UEs may alreadybe able to transmit and/or receive these physical channels and signals,which may reduce complexity for peer discovery. Various physicalchannels and signals may be used for the proximity detection signal.Some exemplary physical channels and signals that may be used for peerdiscovery are described below.

Wireless network 100 may support a set of physical channels and signalsfor the downlink and another set of physical channels and signals forthe uplink. The physical channels and signals for the downlink anduplink may be dependent on the radio technology supported by wirelessnetwork 100. Table 1 lists a set of physical channels and signals forthe downlink in LTE.

TABLE 1 Physical Channels and Signals for Downlink in LTE PhysicalChannel or Signal Acronym Description Primary PSS Signal used by UEs forcell search and Synchronization acquisition. Signal Secondary SSS Signalused by UEs for cell search and Synchronization acquisition. SignalPhysical Broadcast PBCH Physical channel carrying some system Channelinformation. Physical Downlink PDCCH Physical channel carrying controlControl Channel information on downlink. Physical Downlink PDSCHPhysical channel carrying data for Shared Channel UEs scheduled for datatransmission on downlink. Cell-Specific CRS Reference signal for aspecific cell. Reference Signal Positioning PRS Reference signal tosupport positioning. Reference Signal

A reference signal is a signal that is known a priori by a transmitterand a receiver and may also be referred to as pilot. Different referencesignals may be defined for the downlink and uplink and used fordifferent purposes.

Table 2 lists a set of physical channels and signals for the uplink inLTE.

TABLE 2 Physical Channels and Signals for Uplink in LTE Physical Channelor Signal Acronym Description Physical Random PRACH Physical channelcarrying random access Access Channel preambles from UEs attempting toaccess a wireless network. Physical Uplink PUCCH Physical channelcarrying control Control Channel information on uplink. Physical UplinkPUSCH Physical channel carrying only data or Shared Channel both dataand control information on uplink. Sounding SRS Reference signal used byeNBs for Reference Signal channel quality measurement.

LTE supports other physical channels and signals for the downlink anduplink, which are not listed in Tables 1 and 2 for simplicity. Thephysical channels and signals in Tables 1 and 2 are described in 3GPP TS36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA);Physical Channels and Modulation,” which is publicly available.

FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 milliseconds (ms)) and may bepartitioned into 10 subframes with indices of 0 through 9. Each subframemay include two slots. Each radio frame may thus include 20 slots withindices of 0 through 19. Each slot may include L symbol periods, e.g.,seven symbol periods for a normal cyclic prefix (as shown in FIG. 3) orsix symbol periods for an extended cyclic prefix. The 2L symbol periodsin each subframe may be assigned indices of 0 through 2L−1.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition a frequency range into multiple(N_(FFT)) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (N_(FFT))may be dependent on the system bandwidth. For example, the subcarrierspacing may be 15 kilohertz (KHz), and N_(FFT) may be equal to 128, 256,512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. Each subband may cover a range of frequency,e.g., 1.08 MHz.

The available time frequency resources for each of the downlink anduplink may be partitioned into resource blocks. The number of resourceblocks available in a slot may be dependent on the system bandwidth andmay range from 6 to 110 for system bandwidth of 1.25 MHz to 20 MHz,respectively. Each resource block may cover 12 subcarriers in one slotand may include a number of resource elements. Each resource element maycover one subcarrier in one symbol period and may be used to send onemodulation symbol, which may be a real or complex value.

On the downlink, an OFDMA symbol may be transmitted in each symbolperiod of a subframe. On the uplink, an SC-FDMA symbol may betransmitted in each symbol period of a subframe. An OFDMA symbol may begenerated by (i) mapping modulation symbols and/or reference symbols tosubcarriers used for transmission and mapping zero symbols with a signalvalue of zero to the remaining subcarriers, (ii) performing an inversefast Fourier transform (IFFT) on the mapped symbols to obtaintime-domain samples, and (iii) appending a cyclic prefix to obtain anOFDMA symbol. A SC-FDMA symbol may be generated by (i) performing adiscrete Fourier transform (DFT) on modulation symbols and/or referencesymbols to be transmitted, (ii) mapping the DFT outputs to subcarriersused for transmission and zero symbols to the remaining subcarriers,(iii) performing an IFFT on the mapped symbols to obtain time-domainsamples, and (iv) appending a cyclic prefix to obtain a SC-FDMA symbol.A SC-FDMA symbol may be generated with an additional DFT step that isnot present in the generation of an OFDMA symbol.

In LTE, an eNB may transmit the PSS and SSS on the downlink in thecenter 1.08 MHz of the system bandwidth for each cell supported by theeNB. The PSS and SSS may be transmitted in symbol periods 6 and 5,respectively, in subframes 0 and 5 of each radio frame with the normalcyclic prefix for FDD, as shown in FIG. 3. The PSS and SSS may be usedby the UEs for cell search and acquisition. The eNB may transmit thePBCH in symbol periods 0 to 3 in slot 1 of certain radio frames. ThePBCH may carry some system information.

A subframe for the downlink may include a control region and a dataregion, which may be time division multiplexed as shown in FIG. 3. Thecontrol region may include the first Q symbol periods of the subframe,where Q may be equal to 1, 2, 3 or 4. Q may change from subframe tosubframe and may be conveyed in the first symbol period of the subframe.The control region may carry control information for UEs. The dataregion may include the remaining 2L-Q symbol periods of the subframe andmay carry data and/or other information for UEs.

An eNB may transmit the PDCCH in the control region of a subframe andmay transmit the PDSCH in the data region of the subframe. The PDCCH maycarry control information such as downlink grants, uplink grants, etc.The PDSCH may carry data for UEs scheduled for data transmission on thedownlink. The eNB may also transmit a PRS periodically. The PRS may bemeasured by UEs for positioning.

In LTE, a UE may transmit the PUCCH, PUSCH, and PRACH on the uplink toan eNB. The PUCCH may carry control information. The PUSCH may carryonly data or both data and control information. The PRACH may carryrandom access preambles sent by the UE to access the wireless network.The UE may also transmit a SRS periodically (when and as configured forthe UE). The SRS may be used by the eNB for channel quality measurement.

FIG. 4 shows a design of transmitting proximity detection signals. Inthis design, some subframes may be reserved for transmission ofproximity detection signals by UEs and may be referred to as PDSsubframes. The PDS subframes may be spaced apart by T_(PDS) ms, whichmay be referred to as the PDS periodicity. In general, a proximitydetection signal may be transmitted in any portion of a PDS subframe andin any number of symbol periods in the PDS subframe. The time durationin which the proximity detection signal is transmitted may be dependenton how the proximity detection signal is generated, as described below.In one design, a UE may transmit a proximity detection signal in one ormore resource blocks in a PDS subframe, as described below.

In general, some resources may be reserved for transmission of proximitydetection signals by UEs for peer discovery. The reserved resources maycomprise time-frequency resources, which may correspond to all resourceblocks in certain subframes, or certain bandwidth in some subframes, orcertain symbol periods in some subframes, or time-frequency resourcesdetermined in any manner. The reserved resources may also comprisecertain sequences, codes, and/or other types of resources.

In one design, the amount of resources reserved for transmission ofproximity detection signals may be configurable. For example, 1000,5000, or 20000 resource blocks may be reserved for transmission ofproximity detection signals in light, medium, or high density P2Pdeployments, respectively. In one design, loading on the reservedresources may be measured by UEs and reported to the network. Theloading may be quantified by various metrics, which may be related tostatistics of received power (e.g., mean received power, 5 percentilereceived power, etc.), statistics of the number of peer UEs detected onthe reserved resources, etc. Loading information reported by the UEs maybe used to change (e.g., increase or decrease) the amount of resourcesreserved for transmission of proximity detection signals. The networkmay broadcast information indicative of the reserved resources.

Proximity detection signals may be transmitted on the reserved resourcesin various manners to mitigate interference between these signals. Inone design, a UE may select a reserved resource on which to transmit aproximity detection signal. The reserved resource may be randomlyselected by the UE or selected from among reserved resources having lowdetected signal power. In another design, the UE may transmit theproximity detection signal with a certain probability on a reservedresource selected in a predetermined manner. For example, the UE maytransmit its proximity detection signal in each PDS subframe with aprobability of 1-P_(blank), where P_(blank) is the probability that theUE will not transmit the proximity detection signal.

The use of reserved resources for transmission of proximity detectionsignals may mitigate interference between P2P signals for P2Pcommunication and WAN signals for WAN communication. The reservedresources may be especially desirable for autonomous peer discovery withuncoordinated transmission of proximity detection signals by P2P UEs.The reserved resources may also allow use of interference cancellationand/or other advanced receiver techniques.

In one design, a proximity detection signal may be generated based onthe PUSCH, PUCCH, PDSCH or PDCCH. The proximity detection signal may betransmitted on a minimum resource allocation for the PUSCH, PUCCH,PDSCH, or PDCCH, which may be two resource blocks. The resource blocksused for the proximity detection signal may cover (i) one set of Ksubcarriers in two slots of one subframe without frequency hopping or(ii) two sets of K subcarriers in two slots with frequency hopping. Inone design, K may be equal to 12 for a narrowband proximity detectionsignal transmitted on one pair of resource blocks covering 180 KHz inone subframe. In another design, K may be a multiple of 12 for awideband proximity detection signal transmitted on multiple pairs ofresource blocks. This design may be used to support a larger payload,which may be required or desirable for some applications with moreinformation to send in the proximity detection signal.

FIG. 5 shows a design of a proximity detection signal generated based onthe PUSCH. In this design, the peer detection signal may include aproximity detection reference signal (PD-RS) and a data portion, whichmay be referred to as a proximity detection PUSCH (PD-PUSCH). In onedesign, the PD-RS may occupy resource elements normally occupied by ademodulation reference signal (DMRS) for the PUSCH, and the PD-PUSCH mayoccupy the remaining resource elements for the PUSCH. In the designshown in FIG. 5, the PD-RS may occupy the middle symbol period of eachslot (or symbol periods 3 and 10 for the normal cyclic prefix), and thePD-PUSCH may occupy the remaining symbol periods in the subframe (orsymbol periods 0-2, 4-9, and 11-13). A PD-RS is a reference signal thatmay be used for coherent detection of the PD-PUSCH. The PD-PUSCH maycarry information for the proximity detection signal, e.g.,identification information such as a UE identity (ID) of a UEtransmitting the proximity detection signal, service informationindicative of service(s) requested by the UE and/or service(s) offeredby the UE, location information indicative of the location of the UE,and/or other information.

In one design, information to send in the proximity detection signal maybe encoded based on one of a number of transport block sizes supportedfor the PUSCH for one resource block pair. The coded information may bemapped to modulation symbols based on a predetermined modulation scheme(e.g., QPSK or BPSK). The modulation symbols may then be mapped toresource elements for the PD-PUSCH.

In one design, the PD-RS may be generated based on a reference signal(RS) sequence having good cross-correlation properties. A set of RSsequences may be defined based on different cyclic shifts of a basesequence, which may be a Zadoff-Chu sequence, a computer generatedsequence, etc. This set of RS sequences may be used for the DMRS for thePUSCH. The RS sequence used for the PD-RS may be selected from the setof RS sequences available for the DMRS. Reference symbols (or pilotsymbols) may be generated based on the RS sequence and mapped toresource elements for the PD-RS.

In one design, a SC-FDMA symbol may be generated for each symbol periodin which the PUSCH-based proximity detection signal is transmitted. EachSC-FDMA symbol may be generated based on modulation symbols or referencesymbols mapped to subcarriers used for the proximity detection signaland zero symbols mapped to the remaining subcarriers. The SC-FDMAsymbols for the proximity detection signal may have a single-carrierwaveform and a low peak-to-average-power ratio (PAPR), which may bedesirable. In one design, the SC-FDMA symbols for the proximitydetection signal may be transmitted using a single antenna port, whichmay simplify operation of a P2P UE.

FIG. 6A shows a design of a proximity detection signal generated basedon the PUCCH for format 1/1a/1b in LTE. In this design, the peerdetection signal may include a PD-RS and a data portion, which may bereferred to as a proximity detection PUCCH (PD-PUCCH). The PD-RS mayoccupy resource elements normally occupied by the DMRS for the PUCCH,and the PD-PUCCH may occupy the remaining resource elements for thePUCCH. For PUCCH format 1/1a/1b, the PD-RS may occupy symbol periods 2-4in each slot of a subframe, and the PD-PUCCH may occupy the remainingsymbol periods in the subframe.

FIG. 6B shows a design of a proximity detection signal generated basedon the PUCCH for format 2/2a/2b in LTE. For PUCCH format 2/2a/2b, thePD-RS may occupy symbol periods 1 and 5 in each slot of a subframe, andthe PD-PUCCH may occupy the remaining symbol periods in the subframe.

In one design of a proximity detection signal generated based on PUCCHformat 1/1a/1b, information to send in the proximity detection signalmay be mapped to one modulation symbol, and a RS sequence may bemodulated based on the modulation symbol and spread with an orthogonalsequence to obtain multiple modulated RS sequences. In one design of aproximity detection signal generated based on PUCCH format 2/2a/2b,information to send in the proximity detection signal may be mapped tomultiple modulation symbols, and a RS sequence may be modulated witheach the multiple modulation symbols to obtain one of multiple modulatedRS sequences. For all PUCCH formats, each modulated RS sequence may bemapped to K resource elements in one symbol period. The PD-RS may begenerated based on the RS sequence. A SC-FDMA symbol may be generatedfor each symbol period in which the PUCCH-based proximity detectionsignal is transmitted.

In LTE, an eNB may transmit data (i) in a unicast manner to specific UEsin normal subframes and (ii) in a broadcast manner to all UEs or in amulticast manner to groups of UEs in multicast/broadcast singlefrequency network (MBSFN) subframes. The PDSCH may have differentformats for the normal subframes and MBSFN subframes.

FIG. 7A shows a design of a proximity detection signal generated basedon the PDSCH in a normal subframe. In this design, the peer detectionsignal may include a PD-RS and a data portion, which may be referred toas a proximity detection PDSCH (PD-PDSCH). In one design, the PD-RS mayoccupy resource elements normally occupied by a UE-specific referencesignal (UE-RS) for the PDSCH. The PD-RS may occupy a first set ofsubcarriers in symbol periods 3 and 9 and a second set of subcarriers insymbol periods 6 and 12, with the subcarriers in the second set beingstaggered with respect to the subcarriers in the first set. FIG. 7Ashows a case in which the PD-RS may be transmitted from antenna port 5on resource elements with label “R₅” in FIG. 7A. The PD-RS may also betransmitted from other antenna ports, e.g., from one or more of antennaports 5 to 14 defined in LTE Release 10. In another design, the PD-RSmay occupy resource elements normally occupied by the CRS for the PDSCH.For both designs, the PD-PDSCH may occupy the remaining resourceelements for the PDSCH.

In one design, information to send in the proximity detection signal maybe encoded and mapped to modulation symbols, e.g., based on apredetermined modulation scheme. The modulation symbols may then bemapped to resource elements for the PD-PDSCH. In one design, the PD-RSmay be generated based on a RS sequence in similar manner as for theUE-RS with the following difference. A RS sequence for the UE-RS may begenerated based on a pseudo-random number (PN) sequence and a cell ID,which may be within a range of 0 to 503. In one design, a RS sequencefor the PD-RS may be generated based on a PN sequence and a UE ID (or adummy cell ID), which may be within a range of 0 to S, where S may belarger than 511. The RS sequence for the PD-RS may thus be differentfrom the RS sequence for the UE-RS. In one design, a set of RS sequencesmay be defined for the PD-RS, and one RS sequence in this set may beselected for the PD-RS (e.g., randomly by a UE). Reference symbols maybe generated based on the selected RS sequence and mapped to resourceelements for the PD-RS.

In one design, an OFDMA symbol may be generated for each symbol periodin which the PDSCH-based proximity detection signal is transmitted. EachOFDMA symbol may be generated based on modulation symbols and/orreference symbols mapped to subcarriers used for the proximity detectionsignal and zero symbols mapped to the remaining subcarriers. In onedesign, the OFDMA symbols for the proximity detection signal may betransmitted from one or more antenna ports. The PD-RS may occupyresource elements corresponding to the antenna port(s) from which theproximity detection signal is transmitted.

FIG. 7B shows a design of a proximity detection signal generated basedon the PDSCH in a MBSFN subframe. In this design, the PD-RS may occupyresource elements normally occupied by a MBSFN reference signal(MBSFN-RS) and may be transmitted from antenna port 4 on resourceelements with label “R₄” in FIG. 7B. The PD-PDSCH may occupy theremaining resource elements for the PDSCH.

In one design, information to send in the proximity detection signal maybe encoded and mapped to modulation symbols, which may then be mapped toresource elements for the PD-PDSCH. In one design, the PD-RS may begenerated based on a RS sequence in similar manner as for the MBSFN-RSwith the following difference. A RS sequence for the MBSFN-RS may begenerated based on a PN sequence and a MBSFN area ID. In one design, aRS sequence for the PD-RS may be generated based on a PN sequence and aUE ID and may have a length of 3K/2 (e.g., a length of 18 for 12subcarriers). The RS sequence for the PD-RS may be different from the RSsequence for the MBSFN-RS. In one design, a set of RS sequences may bedefined for the PD-RS, and one RS sequence in this set may be selectedfor the PD-RS (e.g., randomly by a UE). Reference symbols may begenerated based on the selected RS sequence and mapped to resourceelements for the PD-RS.

FIG. 8 shows a design of a proximity detection signal generated based onthe PDCCH in a normal subframe. In this design, the peer detectionsignal may include a PD-RS and a data portion, which may be referred toas a proximity detection PDCCH (PD-PDCCH). In one design, the PD-RS mayoccupy resource elements normally occupied by the CRS. The PD-PDCCH mayoccupy all resource elements not used for the CRS in the control regionof a subframe. In one design, the control region may cover a fixednumber of symbol periods (e.g., three symbol periods) in a subframereserved for transmission of proximity detection signals. In one design,information to send in the proximity detection signal may be encoded andmapped to modulation symbols, which may then be mapped to resourceelements for the PD-PDCCH.

In one design, a proximity detection signal may be generated based onthe PSS and SSS and may be transmitted in a sequence of possiblynon-contiguous subframes. The PSS and SSS may be well suited for peerdetection and initial synchronization since they are specificallydesigned for cell search and acquisition in LTE.

The PSS and SSS may be transmitted by eNBs to assist WAN UEs performcell search and acquisition. A proximity detection signal may begenerated by a P2P UE based on the PSS and SSS and transmitted in amanner to avoid confusion with reception of the PSS and SSS from eNBs byWAN UEs. This may be achieved based on one or more of the following:

-   -   Transmit a proximity detection signal at a frequency that is not        used for the PSS and SSS transmitted by eNBs, e.g., offset from        a channel raster,    -   Transmit a proximity detection signal on uplink spectrum instead        of downlink spectrum in a FDD deployment,    -   Transmit the PSS and SSS in a proximity detection signals in        symbol locations different from the locations in which the PSS        and SSS are transmitted by eNBs,    -   Scramble the SSS in a proximity detection signal with a        different scrambling sequence than the one used for the SSS        transmitted by eNBs, and    -   Transmit a cyclic redundancy check (CRC) with a proximity        detection signal.        The features listed above are described in further detail below.

P2P UEs may be synchronized to the wireless network, which may bebeneficial to allow the P2P UEs to time division multiplex between WANcommunication and P2P communication without significant resourcewastage. If P2P UEs are synchronized to the wireless network andtransmit their proximity detection signals comprising the PSS and SSS inthe center 1.08 MHz (i.e., the middle six resource blocks), then WAN UEsmay confuse the PSS and SSS from the P2P UEs with the PSS and SSS fromeNBs. Confusion between the PSS and SSS from P2P UEs and the PSS and SSSfrom eNBs may be addressed in various manners.

In one design, a P2P UE may transmit a proximity detection signalcomprising the PSS and SSS at a frequency that is not used to transmitthe PSS and SSS by any eNB. The wireless network may utilize a channelraster of 100 kHz for all frequency bands, which means that a carriercenter frequency (i.e., the center of the system bandwidth) must be aninteger multiple of 100 kHz. Frequencies that are spaced apart by thechannel raster may be referred to as channel raster frequencies. Thecarrier center frequency must be one of the channel raster frequencies.In LTE, an eNB may transmit the PSS and SSS on six resource blockscentered at the carrier center frequency. Hence, the center frequency ofthe PSS and SSS is an integer multiple of 100 kHz. Transmitting the PSSand SSS in the center six resource blocks results in the frequencymapping of the PSS and SSS to be invariant with respect to the systembandwidth, which may range from 6 to 110 resource blocks. This allowsWAN UEs to synchronize to the wireless network without the need for apriori knowledge of the system bandwidth.

FIG. 9 shows a design of transmitting a proximity detection signal on anon-raster channel frequency to avoid confusion between the PSS and SSSfrom P2P UEs and the PSS and SSS from eNBs. A non-raster channelfrequency may be any frequency that is not an integer multiple of achannel raster, i.e., not an integer multiple of 100 kHz in LTE. An eNBmay transmit its PSS and SSS on the center 72 subcarriers (correspondingto six resource blocks) in the center of the system bandwidth. The PSSand SSS may thus be centered at the carrier center frequency, as shownin FIG. 9. The spacing between subcarriers may be denoted as Δf and maybe equal to 15 kHz in LTE. In one design, the center frequency of aproximity detection signal (i.e., the PDS center frequency) may beoffset from the carrier center frequency by N_(offset) subcarriers,where N_(offset) may be selected such that N_(offset)*Δf is not aninteger multiple of the channel raster of 100 kHz in LTE. Hence,N_(offset) may be selected such that the PDS center frequency does notcorrespond to any channel raster frequency. In this design, a P2P UEsearching for a proximity detection signal will not detect the PSS andSSS transmitted by eNBs. Similarly, a WAN UE performing cell search onchannel raster frequencies will not detect proximity detection signalstransmitted by P2P UEs.

In general, N_(offset) may be selected such that the PDS centerfrequency is not an integer multiple of the channel raster of any radiotechnology (e.g., LTE, UMTS, etc.) used by the wireless network. Thismay minimize impact due to the proximity detection signals on cellsearch for all radio technologies utilized by the wireless network.

In one design, the network may provide a list of center frequencies thatcan be used as the PDS center frequency and hence should be scanned todetect for proximity detection signals transmitted by P2P UEs. This listmay be broadcast in system information or provided to P2P UEs in othermanners. In one design, the list of PDS center frequencies to be scanneddoes not include any channel raster frequency. This design may avoidtransmission of the PSS and SSS on a raster channel frequency by P2P UEsand may avoid false alarms by WAN UEs.

FIG. 10 shows a design of transmitting the PSS and SSS in a proximitydetection signal in different symbol locations to avoid confusion withthe PSS and SSS from eNBs. An eNB may transmit the PSS and SSS in symbolperiods 6 and 5, respectively, of subframes 0 and 5 in FDD, as shown bya waveform 1010. An eNB may transmit the PSS in symbol period 2 ofsubframes 1 and 6 and the SSS in symbol period 13 of subframes 0 and 5in TDD, as shown by a waveform 1012. In one design that is shown in FIG.10, the positions of the PSS and SSS in a proximity detection signal maybe swapped relative to the positions of the PSS and SSS transmitted byan eNB. In this design, a P2P UE may transmit the PSS and SSS in symbolperiods 5 and 6, respectively, in FDD, as shown by a waveform 1014. AP2P UE may transmit the PSS in symbol period 13 of subframes 0 and 5 andthe SSS in symbol period 2 of subframes 1 and 6 in TDD, as shown by awaveform 1016.

In another design, the PSS and SSS in a proximity detection signal maybe sent at TDD symbol locations in a FDD deployment and at FDD symbollocations in a TDD deployment. Hence, if wireless network 100 utilizesFDD, then an eNB may transmit its PSS and SSS as shown by waveform 1010,and a P2P UE may transmit the PSS and SSS in the proximity detectionsignal as shown by waveform 1012. Conversely, if wireless network 100utilizes TDD, then an eNB may transmit its PSS and SSS as shown bywaveform 1012, and a P2P UE may transmit the PSS and SSS in theproximity detection signal as shown by waveform 1010.

The designs described above may enable P2P UEs to reuse most of a cellsearcher to detect proximity detection signals. For example, a P2P UEmay use the cell searcher to detect PSS and SSS from eNBs at symbollocations defined for FDD and detect PSS and SSS from P2P UEs at symbollocations defined for TDD.

In yet another design, the spacing between the PSS and SSS in aproximity detection signal may be different than the spacing between thePSS and SSS transmitted by eNBs. For example, in a FDD deployment, thespacing between the PSS and SSS in a proximity detection signal may beincreased to two slots while maintaining the PSS at the same symbollocation (i.e., the same slot and radio frame positions) as the PSStransmitted by eNBs. The PSS and SSS in a proximity detection signal mayalso be sent in other symbol locations different from the symbollocations of the PSS and SSS transmitted by eNBs.

In another design, a proximity detection signal may be transmitted at anon-raster channel frequency and also in different symbol locations toavoid confusion between the PSS and SSS from P2P UEs and the PSS and SSSfrom eNBs. For example, in a FDD deployment, a P2P UE may transmit thePSS and SSS in its proximity detection signal in symbol locations shownby waveform 1016 in FIG. 10 and at a PDS center frequency that may beoffset by 50 kHz from the channel raster.

In one design, the SSS in a proximity detection signal may be scrambledwith a different scrambling sequence than the one used for the SSStransmitted by an eNB. A symbol sequence for the SSS may be generated asfollows:

$\begin{matrix}{{d( {2n} )} = \{ \begin{matrix}{{s_{0}^{(m_{0})}(n)} \cdot {c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{1}^{(m_{1})}(n)} \cdot {c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} } & {{Eq}\mspace{14mu} (1)} \\{{d( {{2n} + 1} )} = \{ \begin{matrix}{{s_{1}^{(m_{1})}(n)} \cdot {c_{1}(n)} \cdot {z_{1}^{(m_{0})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{0}^{(m_{0})}(n)} \cdot {c_{1}(n)} \cdot {z_{1}^{(m_{1})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} } & {{Eq}\mspace{14mu} (2)}\end{matrix}$

where

d(2n) denotes even-numbered symbols in the sequence,

d(2n+1) denotes odd-numbered symbols in the sequence,

s₀ ^((m) ⁰ ⁾(n) and s₁ ^((m) ¹ ⁾(n) denote two cyclic shifts of anm-sequence,

c₀(n) and c₁(n) denote two scrambling sequences,

z₁ ^((m) ⁰ ⁾ _((n)) and z₁ ^((m) ¹ ⁾(n) denote two additional scramblingsequences.

As shown in equations (1) and (2), the SSS may be generated byinterleaving, in the frequency domain, two BPSK modulated secondarysynchronization sequences d(2n) and d(2n+1) of length 31. Sequence d(2n)is also referred to as SSC1, and sequence d(2n+1) is also referred to asSSC2. In each SSS transmission, SSC1 and SSC2 are scrambled by differentscrambling sequences c₀(n) and c₁(n), respectively, which are dependenton the PSS. SSC2 is further scrambled by a sequence z₁ ^((m) ⁰ ⁾(n) orz₁ ^((m) ¹ ⁾(n) that depends on SSC1. In one design, to furtherdistinguish the SSS in a proximity detection signal from the SSStransmitted by eNBs, different scrambling sequences may be used for SSC2by P2P UEs and eNBs and/or different scrambling sequences may be usedfor SSC1 by P2P UEs and eNBs.

An eNB may generate the PSS and SSS based on various sequences, whichmay be determined based on a physical cell ID (PCI) of a cell. The PCImay thus be conveyed in the PSS and SSS transmitted by the eNB. The eNBmay also generate the CRS based on a PN sequence, which may beinitialized based on the PCI. The eNB may transmit the CRS on resourceelements determined based on the PCI in each normal subframe.

In one design, a P2P UE may transmit a CRS along with the PSS and SSS ina proximity detection signal. The CRS may be used as a virtual CRC checkfor the proximity detection signal. In particular, a receiving P2P UEmay detect the proximity detection signal, extract an ID sent in the PSSand SSS, and verify this ID based on the CRS for a virtual CRC check.The virtual CRC check may be beneficial to reduce false alarms and maybe especially desirable in a P2P environment since the number of PDStransmissions may be quite large. The CRS may also be used by thereceiving P2P UE for automatic gain control (AGC) to adjust it receivergain to the proper level. If the CRS is not transmitted, then thereceiving P2P UE may perform AGC based on the first transmission of aproximity detection signal and may perform detection based on one ormore subsequent transmissions of the proximity detection signal, whichmay delay peer detection.

In another design, a proximity detection signal may include an explicitCRC instead of (or in addition to) the CRS. In one design, CRC bits maybe sent on resource elements normally used to transmit the CRS. The CRCbits may also be transmitted at the same power level as (or at a fixedpower offset from) the PSS and SSS and may be used for AGC setting byreceiving P2P UEs.

Information to send in a proximity detection signal may be conveyed viathe PSS and SSS included in the proximity detection signal. For example,the PSS and SSS may be generated by an eNB based on a cell ID having avalue within a range of 0 to 503, as described in LTE Release 8. It maybe desirable to send more information than the amount that can be senton the PSS and SSS by the eNB. In one design, a proximity detectionsignal may include the PSS and SSS as well as the PBCH. In this design,the extra information that cannot be sent in the PSS and SSS may be sentinstead on the PBCH. In one design, a set of IDs (e.g., IDs of 0 to 503)may be supported with the PSS and SSS, and all or a subset of these IDsmay be associated with additional information sent on the PBCH. The IDsassociated with PBCH transmission as a part of a proximity detectionsignal may be either statically assigned or dynamically indicated by thenetwork, e.g., broadcast in system information or sent via upper layersignaling.

In general, the PSS and SSS may be used for proximity detection signalswith both autonomous and network-assisted peer discovery. It may bedesirable to use the PSS and SSS for proximity detection signals inautonomous peer discovery. The P2P UEs may not be within networkcoverage when performing autonomous peer discovery and may need toacquire timing and system information from peer UEs. The use of the PSSand SSS for proximity detection signals may allow the P2P UEs to reuseexisting initial cell search procedure for discovery of peer UEs.

Proximity detection signals generated based on the PSS and SSS may havecertain advantages. First, timing and frequency offsets betweendifferent P2P UEs may be easily tracked based on the proximity detectionsignals. Second, the proximity detection signals may work well in bothtightly-controlled and loosely-controlled network-assisted peerdiscovery. Third, the proximity detection signals may be detectable atvery low signal-to-noise ratio (SINR), especially if interferencecancellation is used. For example, if proximity detection signals fromtwo UEs collide on a certain resource, then the stronger proximitydetection signal may be detected and decoded first, then theinterference due to the stronger proximity detection signal may beestimated and canceled, and the weaker proximity detection signal maythen be detected and decoded.

In one design, a proximity detection signal may be generated based on apositioning reference signal (PRS) normally transmitted on the downlinkby an eNB. The PRS for the proximity detection signal may be transmittedon a configurable bandwidth, which may be referred to as a PRSbandwidth. The PRS bandwidth may be selected based on a tradeoff betweendetection performance and overhead.

FIG. 11 shows a design of a proximity detection signal generated basedon the PRS. In this design, the peer detection signal may occupyresource elements normally occupied by the PRS transmitted by an eNB(e.g., darkened resource elements that are offset by two subcarriersfrom resource elements with label “R₆” in FIG. 11). The proximitydetection signal may be transmitted from antenna port 6 or some otherantenna port. As shown in FIG. 11, the proximity detection signal may betransmitted in symbol periods 3, 5, 6, 8, 9, 10, 12 and 13 of asubframe. The proximity detection signal may also be transmitted onsubcarriers that are spaced apart by six subcarriers in each symbolperiod in which the proximity detection signal is transmitted. Theproximity detection signal may be transmitted on resource elements thatare staggered across time and frequency to facilitate timing andfrequency tracking. Up to six UEs may be multiplexed on the same PRSbandwidth and may transmit their proximity detection signals ondifferent subcarriers.

In one design, some bandwidth may be reserved for transmission ofproximity detection signals based on the PRS. The reserved bandwidth maybe cleared of transmissions from eNBs and WAN UEs in order to avoidinterference to proximity detection signals from P2P UEs.

In one design, a proximity detection signal may be generated based on aSRS normally transmitted on the uplink by a WAN UE. The SRS for theproximity detection signal may be transmitted in one symbol period on aconfigurable bandwidth, which may be referred to as a SRS bandwidth. Forexample, the SRS bandwidth for a SRS transmission may range from 48 to576 subcarriers for 10 MHz system bandwidth. A SRS transmission may alsobe sent on fewer subcarriers (e.g., 12 subcarriers) or more subcarriers.

FIG. 12 shows a design of a proximity detection signal generated basedon the SRS. In this design, the peer detection signal may occupyresource elements normally occupied by the SRS transmitted by a WAN UE(e.g., darkened resource elements in FIG. 12). As shown in FIG. 12, theproximity detection signal may be transmitted in the last symbol periodof a subframe and on subcarriers that are spaced apart by S subcarriers,where S may be 8 or smaller. Up to S different P2P UEs may bemultiplexed in the same symbol period and may transmit their proximitydetection signals on different subcarriers. Different sets of P2P UEsmay transmit their proximity detection signals in different symbolperiods of a subframe. In one design, some resources may be allocatedfor transmission of SRS by UEs, and some of these SRS resources may bereserved for transmission of proximity detection signals by P2P UEs.

Proximity detection signals generated based on the SRS may have certainadvantages. First, since each such proximity detection signal may betransmitted in one symbol period, proximity detection signalstransmitted by P2P UEs with large timing offsets (e.g., of more than onesymbol period) may not interfere one other. Second, the proximitydetection signals may be used to track timing offsets where P2P UEs havedifferent propagation delay. Third, the SRS may have some processinggain in the frequency domain and may be able to tolerate interference toa certain extent. Fourth, the SRS may be used for interferencemanagement between P2P UEs and WAN UEs.

In one design, a proximity detection signal may be generated based on aPRACH normally transmitted on the uplink by a WAN UE. The PRACH for theproximity detection signal may be transmitted in one subframe on apredetermined bandwidth of six resource blocks, which may be referred toas a PRACH bandwidth.

FIG. 13 shows a design of a proximity detection signal generated basedon the PRACH. In this design, the peer detection signal may comprise acyclic prefix of T_(CP) samples followed a preamble sequence of T_(SEQ)samples. T_(CP) and T_(SEQ) may have different values for differentpreamble formats applicable for the PRACH. For the PRACH, a set of 64preamble sequences may be available for use for random access to thewireless network. A WAN UE may select one preamble sequence from the setand may transmit the selected preamble sequence on the PRACH. In onedesign, the same set of 64 preamble sequences may be used for theproximity detection signals. A P2P UE may select one preamble sequencefrom the set and may transmit the selected preamble sequence as itsproximity detection signal. In another design, a set of preamblesequences may be defined for proximity detection signals and may bedifferent from (and have low correlation with) the set of preamblesequences used for the PRACH. For both designs, the number of P2P UEsthat can be multiplexed on the same PRACH bandwidth may be determined bythe number of preamble sequences (e.g., 64) in the set of preamblesequences available for proximity detection signals.

Interference between the PRACH transmitted by WAN UEs and proximitydetection signals transmitted by P2P UEs may be mitigated in variousmanners. In one design, the same PRACH bandwidth may be used by both theWAN UEs and P2P UEs, but different subframes may be allocated to the WANUEs for transmission of the PRACH and to the P2P UEs for transmission ofthe proximity detection signals. In another design, different PRACHbandwidths may be used for the PRACH transmitted by WAN UEs andproximity detection signals transmitted by P2P UEs. In yet anotherdesign, different sets of preamble sequences may be used by the WAN UEsand P2P UEs.

Proximity detection signals generated based on the PRACH may havecertain advantages. First, the proximity detection signals may have highprocessing gain, may be robust against timing and frequency offsets andinterference from other UEs, and may provide good detection performanceeven at a low SINR. Second, a PRACH transmitter and a PRACH receivernormally used for WAN communication may also be used for transmissionand detection of proximity detection signals generated based on thePRACH with minor changes.

In one design, inter-cell coordination may be performed, and neighboringcells may be allocated different resources for transmission of proximitydetection signals by P2P UEs located near cell boundary in order tomitigate/avoid interference between these P2P UEs. In one design, thedifferent resources may be obtained with time division multiplexing(TDM), and P2P UEs in different cells may transmit their proximitydetection signals in different time periods (e.g., different subframes).In another design, the different resources may be obtained withfrequency division multiplexing (FDM), and P2P UEs in different cellsmay transmit their proximity detection signals on different bandwidths.In yet another design, the different resources may correspond todifferent sets of resource elements (or resource blocks), which may beoffset from one another by one or more subcarriers. P2P UEs in differentcells may then transmit their proximity detection signals on differentresource elements (or resource blocks). In yet another design,interference mitigation may be achieved by having P2P UEs generate theirproximity detection signals with different RS sequences, which maycorrespond to different cyclic shifts of a base sequence.

In general, any of the designs described above may be used forautonomous peer discovery and network-assisted peer discovery. The useof physical channels and signals in a wireless network for proximitydetection signals may provide good performance while reducing complexityat P2P UEs to support peer discovery. Proximity detection signals may betransmitted by P2P servers and/or P2P clients and also on downlinkspectrum and/or uplink spectrum.

P2P UEs may transmit their proximity detection signals at the sametransmit power level (which may simplify estimation of pathloss) or atdifferent transmit power levels. P2P UEs may be able to transmitproximity detection signals generated based on uplink signals andchannels at a higher transmit power level than proximity detectionsignals generated based on downlink signals and channels due to asingle-carrier waveform for the uplink channels and signals. Forexample, a P2P UE may be able to transmit a proximity detection signalgenerated based on the PDSCH at X dBm and to transmit a proximitydetection signal generated based on the PUSCH at X+2 dBm. Transmittingat a higher power level may enable detection of the proximity detectionsignal over longer distances.

In general, any information may be sent in a proximity detection signal.In one design, a set of resources available for proximity detectionsignals may be mapped to a set of temporary short IDs. The availableresources may correspond to different RS sequences for the PRS-based,PUCCH-based, and SRS-based designs. The available resources maycorrespond to different PSS and SSS sequences for the PSS/SSS-baseddesign. The available resources may correspond to the payload in thedata portion for the PUSCH-based, PUCCH-based, PDSCH-based, andPDCCH-based designs. In one design, the set of temporary short IDs maybe mapped to a set of global IDs.

A short ID may correspond to a bit string that may be used to identify atransmitting UE of a proximity detection signal. A short ID may not besufficient to uniquely identify the transmitting UE. Hence, a receivingUE may use other means (e.g., assistance from an eNB or a directoryagent) to uniquely identify the transmitting UE from the detected shortID. Short IDs may be used because some signals cannot carry a largepayload (e.g., the PSS/SSS may carry a 9-bit payload). The receiving UEmay report a PSS/SSS sequence detected by the UE to an eNB, e.g., alongwith the time and frequency location where the PSS/SSS was detected. TheeNB (or the directory agent) may use this information from the receivingUE to deduce a global ID of the transmitting UE.

In another design, a set of available resources may be mapped directlyto a set of global IDs. The mapping of available resources to temporaryshort IDs, the mapping of temporary short IDs to global IDs, and/or themapping of available resources to global IDs may be performed by thenetwork (e.g., an eNB) and signaled to UEs.

FIG. 14 shows a design of a process 1400 for performing peer discoverybased on a physical channel in a wireless network. Process 1400 may beperformed by a UE (as described below) or by some other entity. The UEmay select at least one resource block from among a plurality ofresource blocks reserved for transmission of proximity detection signalsby UEs (block 1412). Each resource block may cover a set of subcarriersin a plurality of symbol periods. The UE may generate a proximitydetection signal occupying the at least one resource block based on aSC-FDMA modulation technique (block 1414). The UE may transmit theproximity detection signal to indicate its presence and to enable otherUEs to detect the UE (block 1416).

In one design of block 1414, the UE may generate a reference signal forat least one symbol period in each of the at least one resource block.In one design, the UE may generate the reference signal based on one ofa set of reference signal sequences reserved for proximity detectionsignals. The UE may generate a data signal for at least one remainingsymbol period in each resource block.

In one design, the UE may encode data to be sent in the proximitydetection signal based on a coding scheme, map the encoded data tomodulation symbols based on a modulation scheme, and generate at leastone SC-FDMA symbol for the at least one remaining symbol period based onthe modulation symbols. The UE may select a modulation and coding schemein a set of modulation and coding schemes supported for datatransmission and may determine the coding scheme and the modulationscheme based on the selected modulation and coding scheme. The UE maygenerate the proximity detection signal for transmission on the PUSCH orPUCCH. The UE may generate the at least one SC-FDMA symbol based on themodulation symbols in different manners for the PUSCH and PUCCH, asdescribed above.

FIG. 15 shows a design of a process 1500 for performing peer discoverybased on a physical channel in a wireless network. Process 1500 may beperformed by a UE (as described below) or by some other entity. The UEmay select at least one resource block from among a plurality ofresource blocks reserved for transmission of proximity detection signalsby UEs (block 1512). The UE may generate a proximity detection signaloccupying the at least one resource block based on an OFDMA modulationtechnique (block 1514). The UE may transmit the proximity detectionsignal to indicate its presence and to enable other UEs to detect the UE(block 1516).

In one design of block 1514, the UE may generate a reference signaloccupying a first set of resource elements in the at least one resourceblock (e.g., resource elements with label “R₅” in FIG. 7A or label “R₄”in FIG. 7B). The UE may generate the reference signal based on one of aset of reference signal sequences reserved for proximity detectionsignals. The UE may generate a data signal occupying a second set ofresource elements in the at least one resource block (e.g., resourceelements without any label or hashing in FIG. 7A or 7B).

In one design, the first set of resource elements for the referencesignal may comprise first and second subsets of resource elements. Thefirst subset of resource elements may occupy a first subset ofsubcarriers (e.g., subcarriers 3, 7 and 11 in FIG. 7A) in at least onesymbol period. The second subset of resource elements may occupy asecond subset of subcarriers (e.g., subcarriers 1, 5 and 9 in FIG. 7A)in at least one other symbol period. The UE may generate referencesymbols based on a reference signal sequence, map a first subset of thereference symbols to the first subset of resource elements, and map asecond subset of the reference symbols to the second subset of resourceelements.

In one design, to generate the data signal, the UE may encode data to besent in the proximity detection signal based on a coding scheme, map theencoded data to modulation symbols based on a modulation scheme, and mapthe modulation symbols to the second set of resource elements in the atleast one resource block. The UE may generate a plurality of OFDMAsymbols based on the mapped modulation symbols. The UE may generate theproximity detection signal for transmission on the PDSCH or PDCCH. TheUE may generate the plurality of OFDMA symbols in different manners forthe PDSCH and PDCCH, as described above.

Various features may be applicable for both process 1400 in FIG. 14 andprocess 1500 in FIG. 15. In one design, neighboring base stations may beallocated different pluralities of resource blocks for transmission ofproximity detection signals by UEs within the coverage of these basestations. In one design, a UE may select at least one resource blockfrom among a plurality of resource blocks allocated to a base stationserving the UE, or a base station detected strongly by the UE, or a basestation selected in some other manner.

In one design, a UE may generate a proximity detection signal occupyingtwo resource blocks in two slots based on SC-FDMA or OFDMA modulationtechnique. The two resource blocks may cover the same set of subcarrierswithout frequency hopping or different sets of subcarriers withfrequency hopping. The UE may also generate the proximity detectionsignal occupying only one resource block or more than two resourceblocks.

In one design, a UE may transmit a proximity detection signal on anuplink spectrum. In other designs, the UE may transmit the proximitydetection signal on a downlink spectrum (e.g., on a portion of adownlink frequency channel reserved for proximity detection signals), oron a dedicated spectrum for P2P communication, etc. In one design, theUE may transmit the proximity detection signal via a single antennaport. In other designs, the UE may transmit the proximity detectionsignal from multiple antenna ports (e.g., from two antenna ports or allantenna ports available at the UE).

FIG. 16 shows a design of a process 1600 for performing peer discoverybased on synchronization signals used in a wireless network. Process1600 may be performed by a UE (as described below) or by some otherentity. The UE may generate a proximity detection signal comprising aPSS and a SSS (block 1612). The UE may transmit the proximity detectionsignal to indicate its presence (block 1614). The UE may generate and/ortransmit the proximity detection signal such that the PSS and SSS in theproximity detection signal avoid collision with a PSS and a SSStransmitted by a base station in a wireless network. This may beachieved in various manners.

In one design, the UE may transmit the proximity detection signal at acenter frequency that is not used for the PSS and SSS transmitted by thebase station, e.g., a center frequency that is not one of the rasterchannel frequencies for the wireless network. In one design, the UE mayselect the center frequency from a set of center frequencies designatedfor transmission of proximity detection signals. In another design, theUE may transmit the PSS and SSS in a spectrum that is not used for thePSS and SSS transmitted by the base station. For example, the UE maytransmit the PSS and SSS on an uplink spectrum or a dedicated spectrumfor P2P communication.

In yet another design, the UE may transmit the PSS and SSS at differentsymbol locations. The UE may transmit the PSS at a first symbol locationnot used for transmitting the PSS by the base station and/or maytransmit the SSS at a second symbol location not used for transmittingthe SSS by the base station. In yet another design, the UE may transmitthe PSS and SSS with different symbol spacing. The UE may transmit thePSS in the first symbol period and may transmit the SSS in the secondsymbol period. The spacing between the first and second symbol periodsmay be different from the spacing between symbol periods in which thePSS and SSS are transmitted by the base station.

In yet another design, the UE may use different scrambling for the SSS.The UE may scramble the SSS with a scrambling sequence that is not usedfor the SSS transmitted by the base station. The UE may also generateand/or transmit the PSS and SSS in other manners such that they aredistinguishable from the PSS and SSS transmitted by the base station.

In one design, the UE may transmit a reference signal in a subframe inwhich the proximity detection signal is transmitted. The referencesignal may be used by other UEs for AGC and also as a virtual CRC forthe proximity detection signal. In another design, the UE may transmitan explicit CRC, e.g., in the PSS, the SSS, and/or a payload of theproximity detection signal.

In one design, the UE may determine symbol periods allocated to aparticular base station (or a cell) with which the UE is associated. Theallocated symbol periods may be designated for transmission of proximitydetection signals by UEs associated with the particular base station.The UE may transmit the proximity detection signal in at least onesymbol period among the symbol periods allocated to the particular basestation. In another design, the UE may determine a frequency rangeallocated to the particular base station with which the UE isassociated. The frequency range may be designated for transmission ofproximity detection signals by UEs associated with the particular basestation. The UE may transmit the proximity detection signal in thefrequency range.

FIG. 17A shows a block diagram of a design of a UE 120 x, which may beone of the UEs in FIG. 1. Within UE 120 x, a receiver 1712 may receiveP2P signals transmitted by other UEs for P2P communication and downlinksignals transmitted by base stations for WAN communication. Atransmitter 1714 may transmit P2P signals to other UEs for P2Pcommunication and uplink signals to base stations for WAN communication.A module 1716 may detect proximity detection signals transmitted byother UEs for peer discovery. A module 1718 may generate a proximitydetection signal for UE 120 x based on any of the designs describedabove. Module 1718 may transmit the proximity detection signal for peerdiscovery.

A module 1720 may support network-assisted peer discovery and mayperform P2P registration with directory agent 140, generate and send P2Prequests, receive notifications, and initiate peer discovery in responseto the notifications. A module 1722 may measure received signal strengthof proximity detection signals from other UEs and reference signals frombase stations. Module 1722 may generate pilot measurement reportscomprising the received signal strengths of detected UEs and basestations of interest and may send the pilot measurement reports, e.g.,to a serving base station. A module 1724 may support P2P communication,e.g., generate and process signals used for P2P communication. A module1726 may support WAN communication, e.g., generate and process signalsused for WAN communication. The various modules within UE 120 x mayoperate as described above. A controller/processor 1728 may direct theoperation of various modules within UE 120 x. A memory 1730 may storedata and program codes for UE 120 x.

FIG. 17B shows a block diagram of a design of a base station 110 x,which may be one of the base stations in FIG. 1. Within base station 110x, a receiver 1742 may receive uplink signals transmitted by UEs for WANcommunication. A transmitter 1744 may transmit downlink signals to UEsfor WAN communication. A module 1746 may receive pilot measurementreports from UEs. A scheduler 1748 may select P2P communication or WANcommunication for UEs based on the pilot measurement reports and mayassign resources to the scheduled UEs. A module 1750 may support WANcommunication for UEs, e.g., generate and process signals used for WANcommunication. A module 1752 may support communication with othernetwork entities (e.g., other base stations, network controllers,directory agent 140, etc.) via the backhaul. The various modules withinbase station 110 x may operate as described above. Acontroller/processor 1754 may direct the operation of various moduleswithin base station 110 x. A memory 1756 may store data and programcodes for base station 110 x.

FIG. 17C shows a block diagram of a directory agent 140 x, which may beone design of directory agent 140 in FIG. 1. Within directory agent 140x, a module 1772 may perform P2P registration for UEs seeking assistancefor peer discovery. A module 1774 may perform request matching toidentify UEs that match other UEs. A module 1776 may send notificationsto matched UEs. A module 1778 may support communication with othernetwork entities (e.g., network controllers) via the backhaul. Acontroller/processor 1780 may direct the operation of various moduleswithin directory agent 140 x. A memory 1782 may store data and programcodes for directory agent 140 x.

The modules within UE 120 x in FIG. 17A, base station 110 x in FIG. 17B,and directory agent 140 x in FIG. 17C may comprise processors,electronic UEs, hardware UEs, electronic components, logical circuits,memories, software codes, firmware codes, etc., or any combinationthereof.

FIG. 18 shows a block diagram of a base station 110 y, a UE 120 y, and adirectory agent 140 y, which may be another design of a UE, a basestation, and directory agent 140 in FIG. 1. Base station 110 y may beequipped with T antennas 1834 a through 1834 t, and UE 120 y may beequipped with R antennas 1852 a through 1852 r, where in general T≧1 andR≧1.

At base station 110 y, a transmit processor 1820 may receive data from adata source 1812 and control information (e.g., messages supporting peerdiscovery) from a controller/processor 1840. Processor 1820 may process(e.g., encode and modulate) the data and control information to obtaindata symbols and control symbols, respectively. Processor 1820 may alsogenerate reference symbols for synchronization signals, referencesignals, etc. A transmit (TX) multiple-input multiple-output (MIMO)processor 1830 may perform spatial processing (e.g., precoding) on thedata symbols, the control symbols, and/or the reference symbols, ifapplicable, and may provide T output symbol streams to T modulators(MODs) 1832 a through 1832 t. Each modulator 1832 may process arespective output symbol stream (e.g., for OFDM, etc.) to obtain anoutput sample stream. Each modulator 1832 may further process (e.g.,convert to analog, amplify, filter, and upconvert) the output samplestream to obtain a downlink signal. T downlink signals from modulators1832 a through 1832 t may be transmitted via T antennas 1834 a through1834 t, respectively.

At UE 120 y, antennas 1852 a through 1852 r may receive the downlinksignals from base station 110 y, downlink signals from other basestations, and/or P2P signals from other UEs and may provide receivedsignals to demodulators (DEMODs) 1854 a through 1854 r, respectively.Each demodulator 1854 may condition (e.g., filter, amplify, downconvert,and digitize) a respective received signal to obtain input samples. Eachdemodulator 1854 may further process the input samples (e.g., for OFDMA,etc.) to obtain received symbols. A MIMO detector 1856 may obtainreceived symbols from all R demodulators 1854 a through 1854 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 1858 may process (e.g., demodulateand decode) the detected symbols, provide decoded data for UE 120 y to adata sink 1860, and provide decoded control information to acontroller/processor 1880. A channel processor 1884 may detect proximitydetection signals from other UEs and may measure the received signalstrength of the detected proximity detection signals.

On the uplink, at UE 120 y, a transmit processor 1864 may receive datafrom a data source 1862 and control information (e.g., messages for peerdiscovery) from controller/processor 1880. Processor 1864 may process(e.g., encode and modulate) the data and control information to obtaindata symbols and control symbols, respectively. Processor 1864 may alsogenerate reference symbols for reference signals. Processor 1864 mayalso generate a proximity detection signal based on any of the designsdescribed above. The symbols from transmit processor 1864 may beprecoded by a TX MIMO processor 1866 if applicable, further processed bymodulators 1854 a through 1854 r (e.g., for SC-FDMA, OFDMA, etc.), andtransmitted to base station 110 y, other base stations, and/or otherUEs. At base station 110 y, the uplink signals from UE 120 y and otherUEs may be received by antennas 1834, processed by demodulators 1832,detected by a MIMO detector 1836 if applicable, and further processed bya receive processor 1838 to obtain decoded data and control informationsent by UE 120 y and other UEs. Processor 1838 may provide the decodeddata to a data sink 1839 and the decoded control information tocontroller/processor 1840.

Controllers/processors 1840 and 1880 may direct the operation at basestation 110 y and UE 120 y, respectively. Processor 1880 and/or otherprocessors and modules at UE 120 y may perform or direct process 1400 inFIG. 14, process 1500 in FIG. 15, process 1600 in FIG. 16, and/or otherprocesses for the techniques described herein. Memories 1842 and 1882may store data and program codes for base station 110 y and UE 120 y,respectively. A communication (Comm) unit 1844 may enable base station110 y to communicate with other network entities. A scheduler 1846 mayschedule UEs for WAN communication and P2P communication and may assignresources to the scheduled UEs.

Within directory agent 140 y, a controller/processor 1890 may performvarious functions to support peer discovery. Controller/processor 1890may perform P2P registration for UEs, receive P2P requests from UEs,perform request matching, and provide notifications to initiate peerdiscovery by matched UEs. A memory 1892 may store program codes and datafor directory agent 140 y. A storage unit 1894 may store information forUEs that have registered with the directory agent, P2P requests from theUEs, etc. A communication unit 1896 may enable the directory agent tocommunicate with other network entities.

In one configuration, apparatus 120 x or 120 y for wirelesscommunication may include means for selecting at least one resourceblock from among a plurality of resource blocks reserved fortransmission of proximity detection signals by UEs, means for generatinga proximity detection signal occupying the at least one resource blockbased on a SC-FDMA modulation technique, and means for transmitting theproximity detection signal by a UE to indicate presence of the UE.

In another configuration, apparatus 120 x or 120 y for wirelesscommunication may include means for selecting at least one resourceblock from among a plurality of resource blocks reserved fortransmission of proximity detection signals by UEs, means for generatinga proximity detection signal occupying the at least one resource blockbased on an OFDMA modulation technique, and means for transmitting theproximity detection signal by a UE to indicate presence of the UE.

In yet another configuration, apparatus 120 x or 120 y for wirelesscommunication may include means for generating a proximity detectionsignal comprising a PSS and a SSS, and means for transmitting theproximity detection signal by a UE to indicate presence of the UE.

In an aspect, the aforementioned means may be processor(s) 1864 and/or1880 at UE 120 y, which may be configured to perform the functionsrecited by the aforementioned means. In another aspect, theaforementioned means may be one or more modules or any apparatusconfigured to perform the functions recited by the aforementioned means.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. A method for wireless communication, comprising: generating aproximity detection signal occupying at least one resource block basedon a single-carrier frequency division multiple access (SC-FDMA)modulation technique, each resource block covering a set of subcarriersin a plurality of symbol periods; and transmitting the proximitydetection signal by a user equipment (UE) to indicate presence of theUE.
 2. The method of claim 1, wherein the generating the proximitydetection signal comprises generating the proximity detection signaloccupying two resource blocks in two slots based on the SC-FDMAmodulation technique.
 3. The method of claim 2, wherein the two resourceblocks cover different sets of subcarriers with frequency hopping. 4.The method of claim 1, wherein the generating the proximity detectionsignal comprises generating a reference signal for at least one symbolperiod in each of the at least one resource block, and generating a datasignal for at least one remaining symbol period in said each of the atleast one resource block.
 5. The method of claim 4, wherein thegenerating the reference signal comprises generating the referencesignal based on one of a set of reference signal sequences reserved forproximity detection signals transmitted by UEs.
 6. The method of claim4, wherein the generating the data signal comprises encoding data to besent in the proximity detection signal based on a coding scheme, mappingthe encoded data to modulation symbols based on a modulation scheme, andgenerating at least one SC-FDMA symbol for the at least one remainingsymbol period based on the modulation symbols.
 7. The method of claim 6,wherein the generating the data signal further comprises selecting amodulation and coding scheme in a set of modulation and coding schemessupported for data transmission, and determining the coding scheme andthe modulation scheme based on the selected modulation and codingscheme.
 8. The method of claim 1, wherein the transmitting the proximitydetection signal comprises transmitting the proximity detection signalon an uplink spectrum.
 9. The method of claim 1, wherein thetransmitting the proximity detection signal comprises transmitting theproximity detection signal via a single antenna port.
 10. The method ofclaim 1, further comprising: selecting the at least one resource blockfrom among a plurality of resource blocks reserved for transmission ofproximity detection signals by UEs.
 11. The method of claim 10, whereinat least two neighboring base stations are allocated differentpluralities of resource blocks for transmission of proximity detectionsignals by UEs within coverage of the base stations.
 12. The method ofclaim 1, wherein the generating the proximity detection signal comprisesgenerating the proximity detection signal for transmission on a PhysicalUplink Shared Channel (PUSCH) or a Physical Uplink Control Channel(PUCCH).
 13. An apparatus for wireless communication, comprising: meansfor generating a proximity detection signal occupying at least oneresource block based on a single-carrier frequency division multipleaccess (SC-FDMA) modulation technique, each resource block covering aset of subcarriers in a plurality of symbol periods; and means fortransmitting the proximity detection signal by a user equipment (UE) toindicate presence of the UE.
 14. The apparatus of claim 13, wherein themeans for generating the proximity detection signal comprises means forgenerating a reference signal for at least one symbol period in each ofthe at least one resource block, and means for generating a data signalfor at least one remaining symbol period in said each of the at leastone resource block.
 15. The apparatus of claim 13, further comprising:means for selecting the at least one resource block from among aplurality of resource blocks reserved for transmission of proximitydetection signals by UEs.
 16. The apparatus of claim 13, wherein themeans for generating the proximity detection signal comprises means forgenerating the proximity detection signal for transmission on a PhysicalUplink Shared Channel (PUSCH) or a Physical Uplink Control Channel(PUCCH).
 17. An apparatus for wireless communication, comprising: atleast one processor configured to generate a proximity detection signaloccupying at least one resource block based on a single-carrierfrequency division multiple access (SC-FDMA) modulation technique, eachresource block covering a set of subcarriers in a plurality of symbolperiods, and to transmit the proximity detection signal by a userequipment (UE) to indicate presence of the UE.
 18. The apparatus ofclaim 17, wherein the at least one processor is configured to generate areference signal for at least one symbol period in each of the at leastone resource block, and to generate a data signal for at least oneremaining symbol period in said each of the at least one resource block.19. The apparatus of claim 17, wherein the at least one processor isconfigured to select the at least one resource block from among aplurality of resource blocks reserved for transmission of proximitydetection signals by UEs.
 20. The apparatus of claim 17, wherein the atleast one processor is configured to generate the proximity detectionsignal for transmission on a Physical Uplink Shared Channel (PUSCH) or aPhysical Uplink Control Channel (PUCCH).
 21. A computer program product,comprising: a non-transitory computer-readable medium comprising: codefor causing at least one processor to generate a proximity detectionsignal occupying at least one resource block based on a single-carrierfrequency division multiple access (SC-FDMA) modulation technique, eachresource block covering a set of subcarriers in a plurality of symbolperiods, and code for causing the at least one processor to transmit theproximity detection signal by a user equipment (UE) to indicate presenceof the UE.
 22. A method for wireless communication, comprising:generating a proximity detection signal occupying at least one resourceblock based on an orthogonal frequency division multiple access (OFDMA)modulation technique, each resource block covering a set of subcarriersin a plurality of symbol periods; and transmitting the proximitydetection signal by a user equipment (UE) to indicate presence of theUE.
 23. The method of claim 22, wherein the generating the proximitydetection signal comprises generating the proximity detection signaloccupying two resource blocks in two slots based on the OFDMA modulationtechnique.
 24. The method of claim 23, wherein the two resource blockscover different sets of subcarriers with frequency hopping.
 25. Themethod of claim 22, wherein each resource block includes a plurality ofresource elements, and each resource element covers one subcarrier inone symbol period, and wherein the generating the proximity detectionsignal comprises generating a reference signal occupying a first set ofresource elements in the at least one resource block, and generating adata signal occupying a second set of resource elements in the at leastone resource block.
 26. The method of claim 25, wherein the generatingthe reference signal comprises generating the reference signal based onone of a set of reference signal sequences reserved for proximitydetection signals transmitted by UEs.
 27. The method of claim 25,wherein the first set of resource elements comprises first and secondsubsets of resource elements, the first subset of resource elementsoccupying a first subset of subcarriers in at least one symbol period,and the second subset of resource elements occupying a second subset ofsubcarriers in at least one other symbol period, and wherein thegenerating the reference signal comprises generating reference symbolsbased on a reference signal sequence, mapping a first subset of thereference symbols to the first subset of resource elements, and mappinga second subset of the reference symbols to the second subset ofresource elements.
 28. The method of claim 25, wherein the generatingthe data signal comprises encoding data to be sent in the proximitydetection signal based on a coding scheme, mapping the encoded data tomodulation symbols based on a modulation scheme, mapping the modulationsymbols to the second set of resource elements in the at least oneresource block, and generating a plurality of OFDMA symbols based on themapped modulation symbols.
 29. The method of claim 22, wherein thetransmitting the proximity detection signal comprises transmitting theproximity detection signal via a designated antenna port.
 30. The methodof claim 22, wherein the transmitting the proximity detection signalcomprises transmitting the proximity detection signal on an uplinkspectrum.
 31. The method of claim 22, further comprising: selecting theat least one resource block from among a plurality of resource blocksreserved for transmission of proximity detection signals by UEs.
 32. Themethod of claim 22, wherein the generating the proximity detectionsignal comprises generating the proximity detection signal fortransmission on a Physical Downlink Shared Channel (PDSCH) or a PhysicalDownlink Control Channel (PDCCH).
 33. An apparatus for wirelesscommunication, comprising: means for generating a proximity detectionsignal occupying at least one resource block based on an orthogonalfrequency division multiple access (OFDMA) modulation technique, eachresource block covering a set of subcarriers in a plurality of symbolperiods; and means for transmitting the proximity detection signal by auser equipment (UE) to indicate presence of the UE.
 34. The apparatus ofclaim 33, wherein each resource block includes a plurality of resourceelements, and each resource element covers one subcarrier in one symbolperiod, and wherein the means for generating the proximity detectionsignal comprises means for generating a reference signal occupying afirst set of resource elements in the at least one resource block, andmeans for generating a data signal occupying a second set of resourceelements in the at least one resource block.
 35. The apparatus of claim33, further comprising: means for selecting the at least one resourceblock from among a plurality of resource blocks reserved fortransmission of proximity detection signals by UEs.
 36. The apparatus ofclaim 33, wherein the means for generating the proximity detectionsignal comprises means for generating the proximity detection signal fortransmission on a Physical Downlink Shared Channel (PDSCH) or a PhysicalDownlink Control Channel (PDCCH).
 37. An apparatus for wirelesscommunication, comprising: at least one processor configured to generatea proximity detection signal occupying at least one resource block basedon an orthogonal frequency division multiple access (OFDMA) modulationtechnique, each resource block covering a set of subcarriers in aplurality of symbol periods, and to transmit the proximity detectionsignal by a user equipment (UE) to indicate presence of the UE.
 38. Theapparatus of claim 37, wherein each resource block includes a pluralityof resource elements, and each resource element covers one subcarrier inone symbol period, and wherein the at least one processor is configuredto generate a reference signal occupying a first set of resourceelements in the at least one resource block, and to generate a datasignal occupying a second set of resource elements in the at least oneresource block.
 39. The apparatus of claim 37, wherein the at least oneprocessor is configured to select the at least one resource block fromamong a plurality of resource blocks reserved for transmission ofproximity detection signals by UEs.
 40. The apparatus of claim 37,wherein the at least one processor is configured to generate theproximity detection signal for transmission on a Physical DownlinkShared Channel (PDSCH) or a Physical Downlink Control Channel (PDCCH).41. A computer program product, comprising: a non-transitorycomputer-readable medium comprising: code for causing at least oneprocessor to generate a proximity detection signal occupying at leastone resource block based on an orthogonal frequency division multipleaccess (OFDMA) modulation technique, each resource block covering a setof subcarriers in a plurality of symbol periods, and code for causingthe at least one processor to transmit the proximity detection signal bya user equipment (UE) to indicate presence of the UE.
 42. A method forwireless communication, comprising: generating a proximity detectionsignal comprising a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS); and transmitting the proximity detectionsignal by a user equipment (UE) to indicate presence of the UE.
 43. Themethod of claim 42, wherein the primary and secondary synchronizationsignals in the proximity detection signal avoid collision with primaryand secondary synchronization signals transmitted by a base station in awireless network.
 44. The method of claim 42, wherein the transmittingthe proximity detection signal comprises transmitting the proximitydetection signal at a center frequency that is not used for primary andsecondary synchronization signals transmitted by a base station.
 45. Themethod of claim 44, further comprising: selecting the center frequencyfrom a set of center frequencies designated for transmission ofproximity detection signals by UEs.
 46. The method of claim 42, whereinthe transmitting the proximity detection signal comprises transmittingthe primary synchronization signal in the proximity detection signal ata first symbol location not used for transmitting a primarysynchronization signal by a base station, and transmitting the secondarysynchronization signal in the proximity detection signal at a secondsymbol location not used for transmitting a secondary synchronizationsignal by the base station.
 47. The method of claim 42, wherein thetransmitting the proximity detection signal comprises transmitting theprimary synchronization signal in the proximity detection signal in afirst symbol period, and transmitting the secondary synchronizationsignal in the proximity detection signal in a second symbol period,wherein a spacing between the first and second symbol periods isdifferent from a spacing between symbol periods in which primary andsecondary synchronization signals are transmitted by a base station. 48.The method of claim 42, wherein the generating the proximity detectionsignal comprises scrambling the secondary synchronization signal in theproximity detection signal with a scrambling sequence not used for asecondary synchronization signal transmitted by a base station.
 49. Themethod of claim 42, wherein the transmitting the proximity detectionsignal comprises transmitting the proximity detection signal on anuplink spectrum.
 50. The method of claim 42, further comprising:transmitting a reference signal in a subframe in which the proximitydetection signal is transmitted.
 51. The method of claim 42, wherein thetransmitting the proximity detection signal comprises determining symbolperiods allocated to a base station with which the UE is associated, theallocated symbol periods being designated for transmission of proximitydetection signals by UEs associated with the base station, andtransmitting the proximity detection signal in at least one symbolperiod among the symbol periods allocated to the base station.
 52. Themethod of claim 42, wherein the transmitting the proximity detectionsignal comprises determining a frequency range allocated to a basestation with which the UE is associated, the frequency range beingdesignated for transmission of proximity detection signals by UEsassociated with the base station, and transmitting the proximitydetection signal in the frequency range.
 53. An apparatus for wirelesscommunication, comprising: means for generating a proximity detectionsignal comprising a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS); and means for transmitting the proximitydetection signal by a user equipment (UE) to indicate presence of theUE.
 54. The apparatus of claim 53, wherein the means for transmittingthe proximity detection signal comprises means for transmitting theproximity detection signal at a center frequency that is not used forprimary and secondary synchronization signals transmitted by a basestation.
 55. The apparatus of claim 53, wherein the means fortransmitting the proximity detection signal comprises means fortransmitting the primary synchronization signal in the proximitydetection signal at a first symbol location not used for transmitting aprimary synchronization signal by a base station, and means fortransmitting the secondary synchronization signal in the proximitydetection signal at a second symbol location not used for transmitting asecondary synchronization signal by the base station.
 56. The apparatusof claim 53, wherein the means for transmitting the proximity detectionsignal comprises means for transmitting the proximity detection signalon an uplink spectrum.
 57. An apparatus for wireless communication,comprising: at least one processor configured to generate a proximitydetection signal comprising a primary synchronization signal (PSS) and asecondary synchronization signal (SSS), and to transmit the proximitydetection signal by a user equipment (UE) to indicate presence of theUE.
 58. The apparatus of claim 57, wherein the at least one processor isconfigured to transmit the proximity detection signal at a centerfrequency that is not used for primary and secondary synchronizationsignals transmitted by a base station.
 59. The apparatus of claim 57,wherein the at least one processor is configured to transmit the primarysynchronization signal in the proximity detection signal at a firstsymbol location not used for transmitting a primary synchronizationsignal by a base station, and to transmit the secondary synchronizationsignal in the proximity detection signal at a second symbol location notused for transmitting a secondary synchronization signal by the basestation.
 60. The apparatus of claim 57, wherein the at least oneprocessor is configured to transmit the proximity detection signal on anuplink spectrum.
 61. A computer program product, comprising: anon-transitory computer-readable medium comprising: code for causing atleast one processor to generate a proximity detection signal comprisinga primary synchronization signal (PSS) and a secondary synchronizationsignal (SSS), and code for causing the at least one processor totransmit the proximity detection signal by a user equipment (UE) toindicate presence of the UE.